The invention relates to rotary combustion engines of the type disclosed in U.S. Pat. No. 2,988,065 granted June 13, 1961 to Wankel et al, and particularly, to such an engine designed for operation as a stratified charge engine, for example, as disclosed in U.S. Pat. No. 3,246,636 granted Apr. 19, 1966 to Bentele and U.S. Pat. No. 3,894,518 granted July 15, 1975 to Gavrun et al.
In such stratified charge engines the fuel discharged by high pressure fuel nozzles strikes the working surfaces of the engine rotor. If the rotor working surfaces are too cool, this causes the formation of heavy carbon deposits on the rotor surfaces as well as the generation of significant smoke in the engine exhaust and increases in the amount of hydrocarbons in the engine exhaust. This is particularly true where the interior of the rotor is cooled by a cooling medium such as oil, for example, as disclosed in U.S. Pat. No. 3,176,915 granted Apr. 6, 1965 to Bentele et al.
Various designs have been proposed in attempts to solve this problem. For example, U.S. Pat. No. 3,359,956 granted Dec. 26, 1967 to Bentele discloses a stratified charge rotary engine in which the rotor working surfaces are provided with a coating of low thermal conductivity so as to increase the temperature of the rotor working surfaces. This serves to decrease the aforementioned carbon debit build-up on the rotor as well as the smoke and hydrocarbons in the engine exhaust. U.S. Pat. No. 3,359,956 to Bentele, however, has the disadvantage in that the rotor coating tends to chip or flake off, particularly if relatively thick coatings are applied to the rotor to provide a coating of significant insulating properties over the rotor. This flaking is probably the result of thermal shock caused by temperature differences between the inner and outer surfaces of the coating during engine operation.
U.S. Pat. No. 3,995,602 granted Dec. 7, 1976 to Burley discloses a rotary engine rotor in which insulating plates are fixed to the rotor working surfaces. However, the plates have to be welded to the rotor around their entire periphery and the plate flexes as its temperature changes.
U.S. Pat. No. 4,067,670 granted Jan. 10, 1978 to Goloff discloses a rotary engine in which each rotor working surface is provided with an insert. However, each insert includes a plurality of separate insert sections, each of which is secured to the rotor by a separate bolt or rivet.
U.S. Pat. No. 4,080,934 granted Mar. 28, 1978 to Jones discloses a stratified charge rotary engine in which the rotor working surfaces are provided with inserts which are separated and thermally insulated from the rotor. However, the design disclosed therein is complicated and expensive because thermal expansion of the insert requires the use a complex flexible bolt securing means.